1. Field of the Invention
The present invention relates to a hard disk drive, and more particularly to a stable data writing method by tracking a head speed.
2. Description of the Related Art
With the high capacity and the high access speed, a hard disk drive is commonly used for an auxiliary memory of a computer system. Such a hard disk drive writes data on tracks arranged along concentric circles on a rotating magnetic disk. The hard disk drive includes a plurality of magnetic heads for reading and writing data from and onto the tracks. Further, the hard disk drive includes a head position servo mechanism for radially moving the magnetic head on the disk to position the magnetic head on a selected one of the tracks. In order to selectively position the magnetic head on a particular track, it is necessary to know current positions of the heads with respect to the respective tracks. Such positional information of the heads, i.e., servo information is provided by using a specific servo pattern read from the magnetic disk. Such a servo pattern is permanently recorded on the magnetic disk when assembling the hard disk drive. The servo pattern is read by the heads and used as positional information of the tracks.
The servo information is commonly provided by an embedded servo system. In accordance with the embedded servo system, the servo information is arranged alternately with data areas on the magnetic disk. The servo information includes track positional information, a track address, and index information. The hard disk drive uses the servo information to position the head on a specific track by way of a track seek and a track following. The track seek is to move the head to a specific target track from the current track, and the track following is to accurately follow a center line of the sought track so as to precisely read and write data from and onto the track. For example, in a hard disk drive adopting the embedded servo system, two bursts are previously recorded, as a part of the servo information, on each track.
An A burst and a B burst are normally alternately recorded on the left and right sides of each track, centering on the track center line. If the head is not precisely positioned on the track center line and inclines toward the A burst, then a detection level of the A burst becomes higher than that of the B burst. On the contrary, if the head inclines toward the B burst, then the detection level of the A burst will be lower than that of the B burst. However, if the head is positioned accurately on the center of the track, then the detection levels of the A and B bursts will be the same. In that case, a difference between the detection levels becomes zero and the hard disk drive determines the deviation of the track with respect to the track center and generates a head position error signal PES which is equal to the difference between the detection levels of the A and B bursts.
If the head inclines toward the A burst, then the head position error signal will have a positive value and if the head inclines toward the B burst, then the head position error signal will have a negative value.
Once the head is on track and the position error signal is equal to zero, hard disk drive can stably read and write data from or onto a data area of the track. However, the head position error signal is hardly ever zero due to vibrations of the magnetic disk and the head. Thus, the head position error signal has a signal level varying according to the deviation of the head and has an on-track offset value range within a specific range. The signal level exceeding the on-track offset value range is called an off-track offset range.
Normally, there is a maximum on-track value and a minimum on-track value of the head position error signal. The write gate pulse for writing data on the disk is enabled only when the head position error signal is within the on-track offset value range. If the head position error signal gets out of the on-track offset value range while writing the data, the track seek will be retried.
However, if the head writes data at the maximum on-track value in the previous sector and writes data at the minimum on-track value in the current sector, then the written data will have an offset value which is twice the maximum deviation so that a movement of the head may become unstable and accordingly, a data error may occur.
The following patents each disclose features in common with the present invention but do not teach or suggest the stable data writing method of the present invention: U.S. Pat. No. 5,285,330 to Masaki, entitled Apparatus For Controlling Moving Speed Of Magnetic Head, U.S. Pat. No. 4,068,269 to Commander et al., entitled Positioning System For Data Storage Apparatus And Record Medium For Use Therewith, U.S. Pat. No. 5,173,647 to Hashimoto, entitled Servo Positioning Circuit, U.S. Pat. No. 5,164,931 to Yamaguchi et al., entitled Method And Apparatus For Control Of Positioning, U.S. Pat. No. 5,126,897 to Ogawa et al., entitled Magnetic Recording/Reproducing Apparatus Capable Of Reducing A Setting Time In A Head Positioning Control Mode, U.S. Pat. No. 5,036,506 to Bierhoff, entitled Record Carrier Scanning Apparatus With Feedback Control System For Controlling Scanning Point Position And Velocity, U.S. Pat. No. 5,428,590 to Ogino, entitled Information Recording And Reproducing Apparatus And Method In Which An Information Recording Or Reproducing Head Seeks A Desired Track On A Recording Medium, U.S. Pat. No. 5,383,068 to Shimizu et al., entitled Head Position Recognition Method, A Speed Calculation Method, And A Head Movement Speed Control Device, U.S. Pat. No. 5,576,909 to Dierkes et al., entitled Method For Positioning A Data Transducer Head In A Rotating Disk Drive Data Storage Device, U.S. Pat. No. 5,521,891 to Nakane, entitled Speed Detection Apparatus, Speed Control Motor, And Track Jump Control Circuit, U.S. Pat. No. 4,679,103 to Workman, entitled Digital Servo Control System For A Data Recording Disk File, U.S. Pat. No. 5,381,282 to Arai et al., entitled Inter-Sample Switching Of Servo Control In Direct Access Storage Devices, and U.S. Pat. No. 4,937,803 to Nakane, entitled Track Acquisition Apparatus And Method With Specified Velocity Pattern.